fix(chat): show table and knowledge base folders in the resource menus (#6190)

Tables and knowledge bases gained folder support, but the chat attachment
menu and the embedded resource menu still listed them flat. Both now render
the same hierarchy the Tables and Knowledge pages show.

Unifies the two near-duplicate workflow/file tree builders into one shared
buildResourceFolderTree plus a spec-driven useResourceTreeSections, so all
four foldered families go through one code path. Items whose folder no
longer resolves now surface at the root instead of vanishing.

Author: waleedlatif1